Projection system

ABSTRACT

An improved electronic image projection system having a container with a conducting interior and a deformable medium in the container which decreases in resistivity with decreases in thickness in the presence of electrical charge on the surface of the medium is provided by using as the deformable medium a polymeric material having as an additive a 9,10-anthracene derivative.

United States Patent m1 Perlowski, Jr.

[ 1 Feb. 6, 1973 1 1 PROJECTIQN SYSTEM [75 Inventor: Edward F.Perlowski, ,Iiz, Baldwinsville, N.Y [73] Assignee: General ElectricCompany [22] Filed: Jan. 28, 1971 21 Appl. No.: 110,519

[51] Int. Cl. ..G02b 5/22, H04n 5/72 [58] Field of Search.....252/380,300, 407, 62.1, 399; 176/33, 40; 117/333; 250/108; 178/7.5 D;

[5 6] References Cited UNITED STATES PATENTS 2,943,147 6/1960 Glenn..'...l78/7.5 D

3,125,634 3/1964 Murray ct a1. .178/7.5 D

3,125,635 3/1964 Murray et al.. 178/7.5 D

3,125,636 3/1964 Klebe ..l78/7.5 D

3,125,637 3/1964 Klebe ..178/7.5 D

3,288,927 11/1966 Plump .....l78/7.5 D

3,317,664 5/1967 Perlowski .....l78/7.5 D 3,317,665 5/1967 Perlowski..178/7.5 D

ELECTRON GUN GTHER PUBLICATIONS Chandrosset al iA'c's', 87:14, m 20,1965 pp. 3,359-3,260 Birks et al., Proc. Roy. Soc. (London), Ser. A,

275( 1360), 135-148( 1963) and Chemical Abstracts,

Vol. 59, p. 5952a, (1963).

Chemical Abstracts, Vol. 64, p. 6898f, (1964), (T.D.S. Hamilton).

Chemical Abstracts, Vol. 65, p. 1,720f, (1966), (Himbuch).

Chemical Abstracts, Vol. 67, p. 103,774t,(1967), (Parker et al.).

Primary Examinerl.eon D. Rosdol Assistant Examiner-Irwin GluckAttorney-Marvin Snyder [57] ABSTRACT An improved electronic imageprojection system having a container with a conducting interior and adeformable medium in the container which decreases in resistivity withdecreases in thickness in the presence of electrical charge on thesurface of the medium is provided by using as the deformable medium apolymeric material having as an additive a 9,10- anthracene derivative.

6 Claims, 2 Drawing Figures SCREEN PATENTEDFEB 6 1975 ELECTRON GUNSCREEN 35 INVENTOR EDWARD F. PERLOW SKI ,JR.

ms ATToflNEY.

PROJECTION SYSTEM This invention relates to a projection system of theelectronic type, and more particularly to an electronic image projectionsystem having a container with a conducting interior and a deformablemedium in the container that decreases in resistivity with decreases inthickness in the medium, the medium having as a radiation mode depressorsubstituted 9,10-anthracene.

There is described in U.S. Pat. No. 2,943,147, June 28, 1960, assignedto the same assignee as the present invention, a projection system ofthe above type employing adeformable medium having a high resistivitywhich is responsive to a velocity-modulated electron beam. Generallyspeaking, this projection system, which is illustrated in FIG. 1 of thedrawing, comprises an evacuated glass envelope containing an electrongun 1 l for producing an electron beam 13 and deflecting it in arectangular raster over the surface of a light transmitting deformablemedium 15 which is within a portion 17 of the transparent container. Anenlarged view of this portion of the assembly is shown in FIG. 2. Thebeam 13 is preferably velocity-modulated by a television signal appliedto the deflection means (not shown) in the electron gun ll. Deformablemedium 15 has a central portion 19 of decreased thickness which isdeformations are a function of the number of electrons deposited by thebeam 13 at the various points on the surface of medium 15. Thus, theamplitudes of these deformations are a function of the modulatedelectron beam 13.

The deformations on the surface of medium 15 are utilized to diffractlight from .a source 23 in an optical system including a lens 24 whichprojects an image of light source 23 on the surface of medium 15 througha bar and slit system 25. Another lens 29 images the slits of system 25on the bars of another bar and slit system 31 if there are nodeformations on the surface of deformable medium 15. However, anydeformations on such surface diffract the transient light so that itpasses through the slits in the system 31 with an intensity thatcorresponds to the amplitudes of the deformations and hence theamplitudes of the applied modulating signal such as a television signal.The light passing through system 29 is imaged by a projection lens 33 onscreen 35 by means of mirror 37.

If a conventional deformable medium is utilized at 15 in the illustratedsystem, the average charge density produces a force on the medium 15that overcomes the surface tension from the excess medium outside theraster area and decreases the portion 19 of medium 15 to zero thickness.Under such conditions, no deformations can be formed and the systembecomes inoperative until the medium is replaced. The above patentteaches that if the medium has the property of decreasing in resistivitywith decreasing thickness, portion 19 does not decrease to zerothickness under the pressure of the charges but maintains a thicknesswhich is a function of the magnitude of charge density on the surface ofthe medium 15. With decrease in resistivity, the

time constant is decreased for the passage of leakage current from thesurface of deformable medium 15 to the conducting coating beneath it.This results in an increase in leakage current, decreasing the chargedensi-- ty on the surface of the medium 15 and somewhat relieving thepressure. Eventually, an equilibrium condition is reached in which thepressure from the charges on the surface of the medium equals thepressure from the surface tension on the excess medium surrounding theraster at which the thickness at this equilibrium condition'ismaintained. The charge density on the surface of the medium neverdecreases to zero because of such leakage because it is continuallybeing replaced by electrons from beam 13.

The deformable compositions described in the aforesaid U.S. Pat. No.2,943,147 as suitable for the medium are required to be transparent, becapable of withstanding electron bombardment without significantdecomposition, have a viscosity at the operating temperature (betweenabout 25 and 150 C) of approximately 100 to 50,000 centistokes, and thedeformable composition must not decompose the conducting coating. Themedium must also have a volume resistivity that varies within the rangeof approximately 10 to 10" ohm-cm., with the average resistivity at thestable thickness being approximately 10 ohm-cm.

Among the deformable media or fluids described in I the above patent arebeeswax, methyl silicone fluids,

methyl silicone fluids containing up to 5 percent of phenyl silicones,methylphenyl silicones containing an average of two methyl and phenylgroups per silicon atom in which the mole ratio of methyl groups tosilicon atoms is greater than 0 and less than 2, etc. However, it hasbeen found that these deformable fluids are not as stable as one woulddesire because under the influence of an electron beam, the deformablemedium or deformable fluids tend to increase in viscosity and withcontinued use in the projection system described above, the viscosityincreases to a point where gel parti 'cles begin to form and thedeformable medium ultimately gels. it is quite obvious that theapparatus can no longer be used with a gelled medium which will notsuitably decrease in thickness. 1

The shortcomings of the above media were alleviated by providingtypically very specific Friedel-Crafts reaction products of benzylchloride and aromatic materials such as biphenyl, naphthalene, tolueneand benzene, including substituted materials of these types. Typicalsuch projection systems are described, for example, in U.S. Pat. No.3,317,664 relating to media which are the reaction product of benzylchloride and naphthalene and in U.S. Pat. No. 3,317,665 relating to theFriedel- Crafts reaction product of benzyl chloride and'biphenylmaterial and in U.S. Pat. No. 3,288,927 relating to such reactionproducts of benzyl chloride and benzene, toluene, etc., the abovepatents being assigned to the same assignee as the present invention.

While material provided by the teaching of the immediately precedingpatents had a desirable long-lived suitable viscosity, it was found thatunder continuous electron bombardment during operating conditions, andparticularly at current densities of about 5 microamperes per squareinch and over, perturbations or disturbances appear in the raster whichdetract from or destroy the image. Such disturbances are commonly knownas radiation modes and considered to result from localized chargeconcentration phenomena and/or radiation damage on the surface of thewriting medium or fluid.

From the above it will be seen that there is a need for materials whichcan be used as medium which are not only characterized by long-lived andsuitable viscosity under the radiation effects of electrons from beam 13but which at the same time are resistant to local radiation damage andperturbations of the medi um surface which detracts from, or destroys,clarity of the image. It is therefore a principal object of theinvention to provide medium materials which are possessed of desirablelong life under irradiation and which are resistant to surface radiationeffects.

It has been unexpectedly found that radiation damage to the surface ofthe writing medium canbe effectively suppressed by addition to themedium of substituted 9,10-anthracene derivatives having the followinggeneral formula where each of R and R is selected from the group consisting of phenyl, benzyl, xenyl, naphthyl and the like. While it is notthe present intention to be bound by any theory as to the mode ofoperation of the present additives, it is believed that they act as asump for a large portion of the electronic energy impinging upon thelight valve or medium surface, the major portion of the beam energybeing diverted from the comparatively weak intra-molecular bonds of. thepolymeric medium or writing fluid to the more stable anthracene nucleus,such diverted energy then being dissipated in less harmful forms such asheat, and light as opposed to the rupturing of chemical bonds or to theestablishing of charged convection cells. lt has been found that thepresent invention is applicable to light valve materials or writingfluids in general, particularly those having a viscosity at theoperating temperature of between about 25 and 150 C of from about 100 to50,000 centistokes and a volume resistivity ranging from about 10 to l0ohm-cm. It is thus particularly applicable to the light valve fluidsmentioned in the above patents which are incorporated herein byreference.

The amount of the above anthracene material required is relatively smalland depends upon the degree of radiation mode suppression desired.Generally speaking, taking this factor into consideration along with thewriting current density to be used, critical depth, mobility and thelike, amounts of from about 0.1 percent to 3.0 percent by weight ofanthracene additive have been found useful.

The following example will illustrate the practice of v the invention,it being realized that it is to be taken as exemplary only and not aslimiting in any way.

EXAMPLE There was added to a polybenzyl toluene material exemplified bythe above U.S. Pat. No. 3,288,927, 2 percent by weight of 9,10-diphenylanthracene, the writing fluid so prepared being incorporated in theillustrated apparatus and operated at a current density of 5 microampsper square inch. It was found that even after 163 microamp minutes persquare inch of operation, the image was clear and free of disturbances.On the other hand, writing fluids of the U.S. Pat. No. 3,288,927polybenzyl toluene type used without the anthracene additive arecharacterized by image clarity disturbing radiation modes appearing onthe raster or fluid surface after less than l0 microamp minutes persquare inch of operation. Additionally, the resulting modification tothe charge conduction process by the 9,l0-diphenyl anthracene additivewas found to reduce perturbations in the surface of the fluid andimprove overall picture quality.

The particular diphenyl anthracene used had a vapor pressure of 2.3 X 10Torr at 25 C and l X 10* Torr at 35C.

There is provided, then, by the present invention an improved electronicprojection system. As described, the deformable writing medium, byreason of the prescribed additives, results in improved projectionsystem operation and picture quality and is capable of operation overlong periods of time at relatively high current densities with little orno loss in image clarity caused by radiation damage to the writingmedium surface. lt will be realized that obvious modifications of theinvention may be made without departing from the spirit or scopethereof.

What is claimed is: v

l. A projection system comprising a container having a conductinginterior, a deformable medium in said container having as a radiationmode suppressant a 9, lO-anthracene derivative represented by thegeneral formula where R and R are each selected from the groupconsisting of phenyl, benzyl, xenyl, and naphthyl, electron beam meansfor producing an electrical charge on the surface of said deformablemedium as a function of an applied electrical signal and cooperatingwith said conducting interior to subject said medium to a deformingforce to produce deformations in the surface of said medium, a lightsource, and an optical system for projecting light from said source as afunction of the deformations in the surface of said medium. 7

2. A projection system as in claim 1 wherein R and R are phenyl groupsso that said radiation mode suppressant comprises 9, IO-diphenylanthracene.

3. A projection system as in claim 1 wherein R and R are benzyl groupsso that said radiation mode suppressant comprises 9, 10-dibenzylanthracene.

4. A projection system as in claim 1 wherein R and R are xenyl groups sothat said radiation mode suppressant comprises 9, lO-dixenyl anthracene.

5. A projection system as in claim 1 wherein R and R are naphthyl groupsso that said radiation mode suppressant comprises 9, IO-dinaphthylanthracene.

6. A projection system as in claim 1 wherein said radiation modesuppressant is selected from the group consisting of 9,10-diphenylanthracene, 9,10-dibenzyl anthracene, 9,10-dixenyl anthracene,9,10-dinaphthyl anthracene, and mixtures thereof.

1. A projection system comprising a container having a conductinginterior, a deformable medium in said container having as a radiationmode suppressant a 9, 10-anthracene derivative represented by thegeneral formula
 2. A projection system as in claim 1 wherein R and R''are phenyl groups so that said radiation mode suppressant comprises 9,10-diphenyl anthracene.
 3. A projection system as in claim 1 wherein Rand R'' are benzyl groups so that said radiation mode suppressantcomprises 9, 10-dibenzyl anthracene.
 4. A projection system as in claim1 wherein R and R'' are xenyl groups so that said radiation modesuppressant comprises 9, 10-dixenyl anthracene.
 5. A projection systemas in claim 1 wherein R and R'' are naphthyl groups so that saidradiation mode suppressant comprises 9, 10-dinaphthyl anthracene.